The present invention relates generally to the quantitative determination of materials contained in fluids, and more particularly to the quantitative analysis of materials contained in fluids using in combination the laser-induced dielectric breakdown spectroscopy technique with a filtration system which traps the material under investigation from the fluid sample (gases, liquids or combinations), thereby concentrating it and improving the limit of detection for this material.
It is known that many vapors and particulates are harmful to humans if inhaled. It is therefore necessary to achieve as close to real-time monitoring of ambient environments for the presence of metallic compounds and other dusts as is possible in order to warn workers involved in fabrication operations, metal processing, mining, etc., of substantial concentrations of harmful material disposed such that there is a significant possibility of bodily intake. For example, beryllium, beryllium oxide, or other beryllium-alloy dusts are especially harmful and occur frequently in the nuclear industry.
Beryllium dust is usually monitored by filtration of contaminated air with subsequent chemical processing of the contaminated filter material followed by atomic absorption spectrochemical analysis of the resulting solution. The beryllium mass so determined is divided by the volume of air passed through the filter to obtain an average concentration. The procedure is time-consuming, requires an analytical laboratory and skilled analytical chemists, and is far from being a real-time monitoring technique.
The apparatus and method of the present invention are based on a combination of the filtration technique mentioned hereinabove and laser-induced dielectric breakdown spectroscopy for quantitative analysis of surfaces or material on surfaces. Light from the breakdown induced on the surface of the impregnated filter is collected, dispersed, time-resolved, and recorded, enabling quantitative analysis of the collected material once the apparatus has been calibrated. The rapid analysis of the filter brings the overall analytical technique much closer to a real-time procedure.
U.S. patent application Ser. No. 342,681, "Method For Spectrochemical Analysis Using Time-Resolved Laser-Induced Breakdown," filed Jan. 26, 1982, is assigned to the same party as the instant invention (U.S. Department of Energy), and discloses the laser-induced dielectric breakdown spectrochemical analysis technique. Thomas R. Loree and Leon J. Radziemski comprise the inventive entity of the earlier application. The present invention is an improvement thereon in that for very low impurity concentrations in the fluid under investigation, the dielectric breakdown spectrochemical analytical procedure by itself has insufficient sensitivity to be of value. However, if the impurity is first concentrated by use of appropriate filters, a concept not disclosed in Loree et al., and the filters then quantitatively analyzed by the aforementioned spectrochemical analytical technique, improved detection limits can be obtained for the combination. Moreover, although the present invention does not quite allow real-time monitoring, it is considerably faster than the previously used wet-chemical spectroscopic technique.